I took a punt on a variable IR filter from Fotga this week to use with the newly converted X-T1 (no, never heard of them either). For £16 though I thought I’d chance it.
Today it is grey, there is 100% cloud cover (also grey) and it is raining gently but persistently so not ideal conditions to test an IR filter but I went anyway. The test shot above with the Fuji X100t (standard JPEG SOOC) shows how un-ideal the light was!
Anyway, I figured that as I was there I’d complete the test anyway even though I knew I’d have to re-test once better conditions were available – which won’t be for a while according to the Met Office!
The filter is rather chunky, not a bad thing with my aged fingers, but screws in very easily and appears to be well made. The outer glass rotates smoothly and there are markings around one quarter of the rim to show the relative strength of the filter. It is marked as being 530nm to 750nm and whilst I have no way of checking this the results from the filter do show a definite graduation from one extreme to the other as can be seen in the contact sheets below.
One thing to notice is that whilst mine has a 77mm filter thread the front thread is somewhat bigger which meant my 77mm lens cap was useless. I use stepping rings so always buy screw-in filters at 77mm so I can then use one filter on all my lenses.
I shot a sequence of ten images, all hand held from the same spot, moving the filter one full “stop” between each frame. I created the following contact sheets using the JPEGs (standard preset) straight from the Fuji X-T1 which as I mentioned yesterday has been converted for full spectrum photography.
I then applied a basic channel swap (swapped Red and Blue channels) to the contact sheet which means that every image has had the same treatment.
I’m particularly looking forward to trying the “530nm” end of the filter on a sunny day as this will produce the strongest false-colour effects and up until now my only option has been a 720nm filter which is mainly used for black & white work although does occasionally render a nice false-colour image too. I have no way of telling if these ratings are accurate of course but at least there is a clear difference between the two extremes and a clearly noticeable transition as the filter is rotated from one 530 through to 750nm.
Finally, another image shot with the Fuji X-T1 with the FOTGA filter on the lens set at 530. This is a false-colour infrared image and the channel swapping was rather more involved this time than my usual basic Blue/Red swap.
The image was converted from the RAW file, channel swapped (Red: R30/B70 Green: G110/B-10 Blue: R85/B15) and then Curves and Levels adjustments. When I get time I will post an overview of how I process these files and what my approach to channel swapping looks like.
I’m looking forward to a bright sunny day, although it seems like I have quite a wait ahead of me!